docs: def skipper(func):
      """Decorator that memorizes base_dir, in_ext and out_ext from OPTIONS
      and skips execution for duplicates."""
      @functools.wraps(func)
      def wrapped():
          """Dummy docstring to make pylint happy."""
          key = (OPTIONS['base_dir'], OPTIONS['in_ext'], OPTIONS['out_ext'])
          if key not in seen:
              seen[key] = func()
          return seen[key]
      seen = {}
      return wrapped